Bonnaud, E.; K. Bourgeois, D. Zarzoso Lacoste, and E. Vidal. Cat impact and management on two Mediterranean sister islands: “the French conservation touch”
Cat impact and management on two Mediterranean sister islands: “the French conservation touch”
E. Bonnaud 1,2 , K. Bourgeois 2, D. Zarzoso Lacoste 2, and E. Vidal 2 1 Ecology Systematic and Evolution, UMR CNRS 8079, Univ Paris Sud, Bât. 362, F 91405 ORSAY Cedex IMEP CNRS.
INTRODUCTION effi cacy and prioritization of cat eradications (Fitzgerald The spread of non indigenous species is considered 1988; Paltridge et al. 1997; Fitzgerald and Turner 2000; second only to habitat destruction in harming native Macdonald and Thom 2001). communities and considered fi rst to impact island The Hyères Archipelago has domestic and feral cat biodiversity (Vitousek et al. 1995; Williamson 1996; populations, and is a major breeding site for Yelkouan Whittaker and Fernández Palacios 2007). shearwater. We studied shearwater population viability in Cats ( Felis catus ) were fi rst introduced to islands in order to conduct relevant feral cat management. the Mediterranean in 9000 BP (Vigne et al. 2004; Driscoll The aims of this study were to: 1) monitor the shearwater et al. 2007), and have since been introduced to islands populations; 2) study cat diet in relation to the shearwater worldwide from the sub Antarctic to the sub Arctic, breeding cycle; 3) evaluate the cat impact on the population including the most arid and mesic islands (Ebenhard 1988; viability of shearwaters; and 4) manage cat populations in Courchamp et al. 2003). They are successful invaders of order to maintain biodiversity on islands. islands because they can survive without access to fresh water, have high fecundity, a high adaptability to novel MATERIALS AND METHODS environments, and have generalist predatory behaviours that allow them to feed on most prey species (Pearre and Study area Maass 1998; Fitzgerald and Turner 2000; Say et al. 2002). This study was conducted on two islands within Cats are one of the most damaging invasive predators on the Hyères Archipelago located in the north western islands (Fitzgerald 1988; Macdonald and Thom 2001) Mediterranean Sea (Fig. 1). Le Levant Island (10.8 km²) and are responsible, at least in part, for 8% of global bird, has a maximum elevation of 140 m above sea level and is mammal and reptile extinctions and a signifi cant threat to 9.15 km from the mainland. It is a military island for 90% almost 10% of critically endangered birds, mammals and of its area; the remaining 10% is occupied by civilians. reptiles (Medina et al. 2011). Port Cros Island (6.40 km²) has been protected by National Seabirds are often badly affected by cat introduction Park status since 1963, has a maximum elevation of 196 on islands (Courchamp et al. 2003; Blackburn et al. m above sea level, and is 15 km from the mainland. The 2004; Donlan and Wilcox 2008), particularly petrels and climate is sub humid, temperate Mediterranean with an shearwaters, due to their lack of predatory defence and average annual rainfall of 582.4 mm and an average annual their high vulnerability to adult mortality (Brooke 2004; temperature of 16.5°C (Levant Island Meteorological Le Corre 2008). Different studies have recently shown Offi ce, 1997–2007). The islands are siliceous, Le Levant that several Puffi nus species, especially those belonging being mainly covered by the typical shrubs of “maquis” to the Manx shearwater P. puffi nus worldwide ‘complex’, vegetation with sparse sclerophyllous oaks ( Quercus ilex ) are seriously threatened by introduced predators (Mayol and halepo pines ( Pinus halepensis ); Port Cros being Serra et al. 2000; Ainley et al. 2001; Cuthbert 2002; Keitt covered by mixed forests of the sclerophyllous oaks and et al. 2002; Martínez Gómez and Jacobsen 2004). The halepo pines. Yelkouan shearwater ( Puffi nus yelkouan ) is endemic to the These islands have long been home to introduced Mediterranean Basin and near threatened and declining vertebrates including cats for two centuries (Pasqualini (IUCN Red List), with a breeding population possibly not 1995), rats ( Rattus rattus ) at least since the Roman period exceeding some thousands of pairs and probably restricted (Ruffi no and Vidal 2010), and rabbits ( Oryctolagus to a few breeding locations, most of which have introduced cuniculus ). The Mediterranean endemic seabird, yelkouan predators (Bourgeois and Vidal 2008). shearwater is represented on Le Levant by 800 1,300 pairs Eradicating cats from islands can protect native species and on Port Cros by 140 180 pairs from a world population from the threat of extinction (Nogales et al. 2004) and likely to be fewer than 15,000 pairs (Bourgeois and Vidal research on the ecology of insular feral cats can improve the 2008).
Pages 395-401 In: Veitch, C. R.; Clout, M. N. and Towns, D. R. (eds.). 2011. Island invasives: eradication and management. IUCN, Gland, Switzerland. 395 Island invasives: eradication and management
Shearwater monitoring to test the difference of the cat diet on both islands, then We monitored 100 shearwater burrows on Port Cros randomisation tests were performed to detect differences in during seven breeding seasons (2003 to 2009) and in 76 cat consumption of each prey thereby allowing comparison burrows during three breeding seasons (2007 to 2009) on of small percentages (PD = observed percentage differences; Le Levant to record the percentage of occupied burrows and Manly 1997). breeding success. Like most seabirds, yelkouan shearwaters have low reproductive output; they start breeding at around Cat impact on yelkouan shearwaters 6 years of age, generally fi rst attempts to breed fail, and To estimate the magnitude of cat predation on they produce only one egg per year (e.g., Brooke 1990). shearwaters, we fi rst calculated the number of shearwaters They arrive at their breeding sites in late October or early eaten each year by the cat population. Since no identical November (Vidal 1985; Zotier 1997), which corresponds parts from two or more shearwaters were found in any one to the prospecting period when birds visit the burrows cat scat, each scat were assumed to be of one bird (Keitt and look for their mate. Egg laying is from mid March to et al. 2002; Cuthbert 2002; Bonnaud et al. 2007). Cats early April, hatching in May and fl edging in July and early usually defecate once per day (Konecny 1987). Thus, the August. mean number of the shearwaters per scat is equivalent to A miniature infrared camera on a stiff coaxial cable was the mean number of shearwaters ingested per day and per cat (NP ). The annual mean number of shearwaters killed “snaked” down each burrow to determine the presence of /d pairs, eggs or chicks (Bourgeois and Vidal 2007). Burrows on Le Levant (NP) by the cat population was calculated as were checked nine times during each breeding season: at follows: the end of the pre laying period, the start, middle and end NP = NP /d × 365 × N cat (1) of the laying and hatching periods, and 15 days before the with N cat : number of cats on the island. beginning and at the middle of the fl edging period. A last Predation rates were calculated assuming: 1) predation check was done at the end of the breeding season to fi nd on prospectors (birds looking for a mate and a burrow) possible corpses and confi rm chick fl edging (Bourgeois (PB) was four times higher than on breeders (birds which 2006). A randomisation test was used to compare the were breeders the next year and the current year) (PP); and percent of occupied cavities between the fi rst year and the 2) predation was exerted on prospectors from age 3 (from last year of our censuses N3 P to N6 +P ) and on breeders (fi rst breeding assumed at 6 years, (Brook 1990)) ( N6 ) Cat diet study +B NP = P × ( N6 ) + P × ( N3 + N4 + N5 + N6 ) (2) The diet of feral cats was studied through scat B +B P P P P +P analysis (Fitzgerald et al. 1991; Bonnaud et al. 2007). We With P P = 4 × P B opportunistically collected scats on sample paths from And NP = number of shearwaters killed per year. October 2002 to August 2004 on Port Cros and from The impact of cat predation on shearwater population October 2006 to August 2008 on Le Levant. Scats were dynamics was assessed by constructing a shearwater collected fi ve times per year: when the shearwaters were demographic population model adapted from Bonnaud prospecting, breeding, hatching, rearing and during their et al. 2009 (see Appendix for the model structure and annual exodus. By removing all scats found in the fi eld and implemented parameters). The value of shearwater breeding excluding very old ones, we assumed that each sampling success without cat predation came from monitoring set represented the cat diet for that period. All scats found burrows in Port Cros colonies during four breeding seasons were reported on a map with a handheld global positioning (2006 to 2009). Cat predation rates were then included in system. This sampling allowed us to determine the cat diet several scenarios depending on cat population estimates during each of the shearwater breeding phases. and taking into account the higher shearwater population Scats were analysed by washing through a 0.5 mm estimates for the both islands (shearwater population of 1) sieve under a stream of hot water and separating all items Le Levant Island = 2600 breeders and 2) Port Cros Island = such as hairs, feathers, bone fragments, teeth, and insect 360 breeders; Bourgeois and Vidal 2008). The demographic chitin (Nogales et al. 1988). Each item was then identifi ed population model was run with ULM (Unifi ed Life by comparison with reference material. The diet results Models) mathematical modelling software (Legendre and were given in frequencies of occurrences and numbers of Clobert 1995) and we conducted Monte Carlo simulations prey. A Pearson χ 2 test for independent samples was used (100 time steps and 1000 trajectories) to account for the uncertainty of several population parameters. Cat management on Port-Cros Island Cat presence on Port Cros constituted a threat to the shearwater population which, at 180 pairs, was already small. A cat management programme was started in January 2004. The presence of human inhabitants, and domestic cats meant that the removal of feral cats should be undertaken using only non lethal methods, i.e. cat living traps checked each morning and evening. Complete cat eradication was not possible due to the persistence of a small domestic cat population located in the village. The trapping campaign was initially concentrated near the shearwater colonies and then extended along all paths, especially where cat scats were found. A sterilisation campaign was conducted on the domestic cats and all new domestic cats arriving were checked for sterilisation. During and after cat control we collected cat scats during selected phases of the shearwater breeding cycle. We used a Mann Whitney U test to compare the number of scats found before the beginning of the cat control and after the last feral cat was caught. These scats Fig.1 Study site, Hyères archipelago (south east of France). were analysed only in order to detect shearwater remains. Study conducted on Port-Cros and Le Levant Island.
396 Bonnaud et al .: Cats on two Mediterranean islands
Table 1 Monitoring of the breeding parameters of the yelkouan shearwater and the percent of occupied nests on Port- Cros and Le Levant Islands. Port-Cros Island (360 breeding birds, 100 burrows monitored) Year survey 2003 2004 2005 2006 2007 2008 2009 mean ± SD Occupied burrows 28 32 41 42 39 40 37 37 % occupied burrows 27.7 31.1 39.8 39.6 37.5 38.8 36.6 35.9 ± 4.7 Hatching success* 70.0 85.7 97.4 89.5 73.7 94.7 91.7 86.1 ± 10.5 Fledging success* 92.9 95.8 83.8 85.3 92.9 91.7 100.0 91.8 ± 5.7 Breeding success* 65.0 82.1 81.6 76.3 68.4 86.8 91.7 78.9 ± 9.6 Le Levant Island (2600 breeding birds, 76 burrows monitored) Year survey 2007 2008 2009 mean ± SD Occupied burrows 33 32 30 32 % occupied burrows 46.5 42.1 41.7 43.4 ± 2.7 Hatching success* 93.8 87.1 93.3 91.4 ± 3.7 Fledging success* 76.7 88.9 89.3 84.9 ± 7.2 Breeding success* 71.9 77.4 83.3 77.5 ± 5.7 * Shown as a percentage of the occupied burrows. Cat diet study Due to the renowned harmful effect of rats on seabirds (e.g., Jones et al. , 2008) we tested whether cat control We collected and analysed 689 scats on Port Cros and affected rodent numbers. As cats preyed mainly upon 200 on Le Levant. Cats on both islands preyed mainly rats on this island (Bonnaud et al. 2007) a meso predator upon introduced mammals. Yelkouan shearwater was the release was possible. We set two lines of 30 traps in two most frequent bird found in the scats (Table 2). Other different areas of the island and set live traps every 10 birds (mainly passerines), reptiles and invertebrates were meters during four consecutive nights for 19 trapping secondary prey. When all prey consumed was considered, signifi cant differences appeared between the cat diets of sessions from December 2004 to August 2008 at three or 2 four months intervals both islands (χ = 314, p < 0.001). The consumption of rabbits (PD = 0.203, p < 0.001) and shearwaters (PD = On Le Levant, other than an awareness campaign about 0.376, p < 0.001) were signifi cantly higher on Le Levant the threat of feral cat presence for island biodiversity, there than on Port Cros and consumption of rats (PD = 0.350, has been no cat management. p < 0.001) and wood mice ( Apodemus sylvaticus ) (PD = 0.322, p < 0.001) were signifi cantly lower. More than RESULTS one mammal per scat was found in scats from Port Cros, Shearwater monitoring mainly rats and wood mice. Less than one mammal per scat was found in scats from Le Levant, the cat diet being Shearwater breeding, monitored on Port Cros from mainly comprised of rabbits and shearwaters. 2003 to 2009 and on Le Levant from 2007 to 2009, showed high breeding parameter values (Table 1). On both islands Regarding cat predation on shearwaters, frequency the percent of occupied nests was low (36% on Port Cros of occurrence was low on Port Cros Island (shearwater and 43% on Le Levant). During the study period, nest remains appeared in 5.9% of scats found) compare to occupation signifi cantly increased on Port Cros (PD = that on Le Levant Island (shearwater remains appeared in 0.149, p = 0.0130) and decreased, but not signifi cantly, 44.3% of scats found). on Le Levant. Hatching success increased on Port Cros Cat impact on yelkouan shearwaters and remained stable on Le Levant. Fledging success was high on both islands but slightly higher on Port Cros where The number of shearwaters eaten per cat per year success in the last year sampled reached 100. The overall reached 162 ± 46 and 22 ± 4 individuals respectively on Le breeding success increased to reach similar values on both Levant and Port Cros. Peaks in predation on shearwaters islands. on both islands were during autumn and winter (October– November and December–February), corresponding to their prospecting period (Fig. 2) and this predation remained high during spring on Le Levant (Fig. 2B). Table 2 Food categories of the cat diet on Port-Cros and Le Levant Islands expressed as frequency of occurrence and the numbers of prey per scat. Port-Cros Island Le Levant Island (August 2002 - August 2004) (August 2006 - August 2008) Frequency of Number of prey per Frequency of Number of prey per Food categories occurrence (%) scat* occurrence (%) scat MAMMALS 91.87 1.57 74.50 0.75 Rattus rattus 77.94 0.95 43.00 0.45 Apodemus sylvaticus 34.69 0.54 2.50 0.03 Oryctolagus cuniculus 6.68 0.09 27.00 0.27 BIRDS 16.69 0.12 51.00 0.51 Puffi nus yelkouan 5.81 0.05 43.50 0.44 other birds 10.89 0.06 7.50 0.08 REPTILES 7.84 0.03 11.50 0.12 INSECTS 11.03 0.05 8.50 0.11 * data only available between August 2003 and August 2004
397 Island invasives: eradication and management
Table 4 Numbers of trap nights and cats trapped during the cat management program conducted on Port-Cros Island. Period Trap nights Cats caught Dec Feb 04 45 2 Feb Apr 04 41 4 Apr Jun 04 89 2 Jun Aug 04 60 1 Aug Oct 04 66 3 Oct Jan 05 190 8 Jan Mar 05 262 4 Mar May 05 134 1 May Aug 05 118 1 Aug Oct 05 132 0 Oct Jan 06 617 2 Jan Mar 06 77 0
decreased, becoming nil by January 2006 despite regular trapping sessions being continued. Subsequently, only neutered domestic cats were seen wandering outside the village and were photographed by cameras placed near paths. No sign of recovery of the cat population was observed. The number of scats found on sampling paths signifi cantly decreased from 0.631 ± 0.119 scats/day before the beginning of cat control to 0.177 ± 0.022 scats/day after the last feral cat was caught (U = 2, p < 0.001). Between August 2004 and August 2005 only one scat was found Fig. 2 Frequencies of occurrences of shearwater remains (in May) and it contained shearwater remains. Cat scats found in cat scats during a 2-year survey on (A) Le Levant found after August 2005 were assumed to belong to the Island (B) on Port-Cros Island. few domestic cats wandering around the island but without evidence that they are preying upon shearwaters The population of cats on Port Cros was estimated Rat trapping success in trap lines varied between as 20 based on trapping data during feral cat removal seasons and years but remained low during both 1978 1987 (Bonnaud et al. 2010). It was impossible to estimate the (mean: 0.068 ± 0.024 rats caught per trap night , Granjon cat population of Le Levant but the small number of scats and Cheylan 1993) and 2004 2008 (mean: 0.112 ± 0.026 found per sampling period suggested that cat density on rats caught per trap night, this study) monitoring periods. this island was lower than on Port Cros. Thus, we tested three scenarios of 5, 10 and 20 individuals (Table 3). Applying equations (1) and (2) we calculated the number DISCUSSION of shearwaters killed per year by cat populations of both Shearwater monitoring islands and the predation rates on breeders and prospectors Yelkouan shearwater breeding populations were (Table 3). reduced to a few individuals, especially on Port Cros, The shearwater demographic population models were due to predation by cats. Bourgeois and Vidal (2007) run using scenarios predicting that: 1) without cat predation and Bourgeois et al. (2008b) showed that these breeding the shearwater populations of both islands showed growth habitats are far from saturation. Both have unoccupied rates higher than 1, and 2) with cat predation all scenarios burrows within colonies and sites suitable for new colony showed decline leading to eventual extinction of the establishment. Cat predation kills more shearwaters when shearwater population. they are in the prospecting stage of the breeding cycle. As breeders they spend little time on the ground and avoid Cat management on Port-Cros Island predation by rapidly entering their burrows (Bourgois et Cat removal started in January 2004, with 28 cats trapped al. 2008a). Despite the presence of predators the breeding over two years (Table 4). Trapping success progressively populations of shearwaters on both islands show high
Table 3 Results of the shearwater demographic models which include cat predation rates according to the size of the
cat population on Port-Cros and Le Levant Islands. Shearwater Pop : size of the shearwater populations, N shear.killed: number of yelkouan shearwater killed per the cat population and per year, Cat Pop : size of the cat populations, PB: cat predation rate on breeding birds, PP: cat predation rate on prospecting birds, λ: growth rate of yelkouan shearwater populations,
Text : predicting time (in years) for yelkouan shearwater population extinction. Port-Cros Le Levant
Shearwater Pop 360 2600
Cat Pop 0 20 0 5 10 20
Nshear. killed 0 431 ± 72 0 810 ± 230 1621 ± 460 3241 ± 920 PB 0 0.386 ± 0.065 0 0.101 ± 0.029 0.202 ± 0.057 0.403 ± 0.115 PP 0 1.544 ± 0.260 0 0.404 ± 0.116 0.808 ± 0.228 1.612 ± 0.460 1.0102 ± 0.7054 ± 0.0064 1.0101 ± 0.8586 ± 0.0001 0.6805 ± 0.0021 0.7331 ± 0.0058 λ 0.0000 0.0000
Text (year) 6.3780 ± 0.0185 53.6820 ± 0.0649 21.1840 ± 0.0671 6.5830 ± 0.0384
398 Bonnaud et al .: Cats on two Mediterranean islands reproductive success (77 to 79% Table 1) when compared Cat management on Port-Cros Island to other shearwater and petrel populations (Brooke 1990; Faced by the strong threat exerted by cats on the yelkouan Hunter et al. 2000; Cuthbert 2002; Dunlop et al. 2002; shearwaters, a cat management campaign was conducted on Le Corre et al. 2002; Jouventin et al. 2003; Igual et al. Port Cros Island. This cat management campaign was, to 2007; Rayner et al. 2007; Pascal et al. 2008). Now that the best of our knowledge, one of the fi rst conducted in the predation is controlled, the settlement of new breeders Mediterranean Basin (Genovesi 2005; Lorvelec and Pascal should increase on Port Cros. 2005). It was also one of the few successfully developed using only non lethal trapping and conserving a domestic Cat diet study population of neutered domestic cats on the island (Nogales Our study supported the common observation that et al. 2004). Non lethal trapping proved to be successful in feral cats are highly generalist predators, able to feed on eradicating the feral cat population and rapidly prevented prey ranging from small insects to birds and mammals cat predation on native threatened species. No feral cats that weigh more than 500 g (Nogales and Medina 1996; were observed or trapped on the island during nearly three Tidemann et al. 1994; Turner and Bateson 2000). However, years following the last feral cat caught in October 2005, cats can specialise on what is available and only a few despite a reduced but continuous trapping campaign. Feral species represented the major part of its diet. Introduced cat control, which started in 2004, resulted in an increase mammals and shearwaters were the prey mainly eaten by in numbers of occupied shearwater burrows and breeding cats on these Mediterranean Islands. The differences in pairs, confi rming that cat predation, being mainly focused cat diet between the two islands are explained by the high on the prospecting period, probably limits the recruitment of frequency of occurrences of rabbits and shearwaters on young breeders (Keitt et al. 2002; Massaro and Blair 2003; Le Levant and the high frequencies of occurrences of rats Peck et al. 2008). Moreover, due to the high probability and wood mice on Port Cros (Bourgeois and Vidal, 2008; of a top down regulated ecosystem on Port Cros, the rat Port Cros National Park pers. comm.). Because rabbits and population on this island was carefully monitored during shearwaters are large prey items, the consumption of one and after cat control (Russell et al. 2009). Rat trapping constitutes the required daily food intake per cat (Bonnaud success values have remained similar to previous values et al. 2007). In contrast the consumption of rodents (rats recorded before cat control (Granjon and Cheylan 1993). and wood mice) generally requires the cat to prey upon This suggests that cat control, while diminishing predation more than one individual and can result in greater diversify pressure on rats, has not led to a signifi cant increase in the in the diet. This indicates that the number of prey items rat population size, nor their impact on seabirds. eaten may provide a trophic index which can be used to evaluate cat impact on prey population dynamics. Implications for conservation On islands with multiple introduced predators and Cat impact on yelkouan shearwaters native prey species, it is commonly suggested that the best The cat diet studies revealed high cat predation during solution is the simultaneous eradication of both introduced the prospecting period of the shearwaters and continuing top and mesopredators to avoid any risk of mesopredator predation throughout the year. Cat predation on the release effect (Simberloff 2001; Zavaleta et al. 2001; shearwaters reached 162 ± 46 and 22 ± 4 individuals per Courchamp et al. 2003; Blackburn 2008). However, when cat per year respectively on Le Levant and Port Cros, introduced predators threaten long lived seabirds, top placing these populations of shearwaters at high risk of predators like cats have larger detrimental effects on their local extirpation. These islands have the largest colonies population dynamics than mesopredators (Le Corre 2008; of yelkouan shearwaters in France, being one of the largest Russell et al. 2009). Moreover, top predator populations in the world (Bourgeois and Vidal 2008). are not the only means of regulating mesopredator Mathematical population dynamic models are a useful populations (Blackwell et al. 2003). Thus, the eradication tool to evaluate the impact of species interactions. Our of top predators should be encouraged simultaneously model predicted annual population growth rates slightly with monitoring the population dynamic of other species greater than one without cat predation, which was consistent that can react to this ecosystem management. Knowing with predictions for populations of other Puffi nus species: that most of the islands of the Mediterranean basin house P. griseus (1.017, Hamilton and Moller 1995; 1.044, Jones feral and domestic cats and native endemic species, this 2002), P. huttoni (0.930–1.050, Cuthbert and Davis 2002), study indicates that even if a complete cat eradication is not P. opisthomelas (1.006, Keitt et al. 2002), P. auricularis feasible, feral cat eradication coupled with the persistence (1.001, Martinez Gómez and Jacobsen 2004) and P. of a neutered domestic cat population can lead to the mauretanicus (1.007, Oro et al. 2004). This suggests that same results as total eradication (Oppel et al. 2011). As the scenario selected for the yelkouan shearwater can be intraguild predation involves complex mechanisms and considered realistic and the model structure suitable. Few often multiple trophic interactions (top down or bottom studies have taken predation on prospecting birds into up processes) (Fukami et al. 2006; Elmhagen and Rushton account. Prospecting birds are probably more vulnerable 2007; Ritchie and Johnson 2009), each management action to cat predation due to their behaviour: wandering on the should be planned after a full review of the main biotic ground and calling outside burrows, rather than entering interactions occurring in the ecosystem considered, so as to the burrow rapidly after landing ( James 1985; Brooke optimise native species conservation (Zavaleta et al. 2001; 1990; Ristow 1998; Bourgeois et al. 2008a; Bonnaud Bonnaud et al. 2009; Russell et al. 2009). et al. 2009). Even with a small cat population included, the shearwater demographic showed a decrease of the ACKNOWLEDGEMENTS shearwater populations. In some cases, cat predation on prospectors was so high it exceeded the number of We are very grateful to the Director and H. Bergere prospectors available, indicating immigration from outside of Port Cros National Park for granting permission for these populations. In summary, our results showed that: this research and to all the park managers, especially 1) these shearwater populations cannot survive if they are S. Dromzée, A. Bonneron and O. Laurent for their hard not supported by immigration; and 2) even if the breeding work in the fi eld, as well as to all those from IMEP and populations have a high breeding success, these small ESE. We would like to thank J. Legrand, N. Bigeard, populations seem to be at a high risk of local extinction and G. Berger for their useful contributions. Funds and due to feral cat predation. support were provided by the Port Cros National Park (ref. 08.031.83400), the European Union and the DIREN PACA via a Life Nature project (ref. LIFE03NAT/F000105) and
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Appendix: Life-cycle representation of the population model for the yelkouan shearwater.
N0 : juvenile age class (from fl edging to age 1); Nx : non prospecting sub adult of age x, Nx P : prospecting sub adult of age x, N6 +B : breeding adult age class, N6 +P : prospecting adult age class, Sx: survival of stage x, bx: percentage of birds of stage x prospecting the colony without breeding, Bs: breeding success, β: sex ratio, F: fecundity, P B: predation rate on breeding birds, P P: predation rate on prospecting birds.
Demographic parameters of the Yelkouan shearwater population (based on Bonnaud et al. 2009). Standard deviations (s.d.) are given for mean values. Population Shearwater population Yelkouan Parameters Values proportions sizes a shearwater S0 : survival of stage Juvenile 0.586 with a stable a age-classes Port-Cros Le Levant S1 : survival of stage 1 0.781 distribution S2 : survival of stage 2 a 0.902 N0 0.161 143 1035 S3 : survival of stage 3 a 0.930 N1 0.093 83 598 S4 : survival of stage 4 a 0.930 N2 0.0715 64 460 S5 : survival of stage 5 a 0.930 N3 0.0466 41 300 S6+ : survival of stage 6+ a 0.930 N3 0.017 15 109 P β: sex ratio b 0.5 N4 0.0104 9 67 Bs : breeding success b 0.808 ± 0.105 N4 0.0479 43 308 P b2 : prospecting birds of stage 2 c 0.267 N5 0.0014 1 9 b3 : prospecting birds of stage 3 c 0.756 N5 0.0237 21 152 P b4 : prospecting birds of stage 4 c 0.911 N6 0.4044 360 2600 +B b5 : prospecting birds of stage 5 c 0.978 N6 0.1232 110 792 c +P b6+ : prospecting birds of stage 6+ 0.261 r: prospecting ads breed next year d 0.96 ± 0.02
Data from: a Perrins et al. 1973; Brooke, 1990; Hamilton and Moller 1995; Hunter et al. 2000; Ainley et al. 2001 ( P. puffinus ); Cuthbert et al. 2001; Jones 2002 ( Puffinus sp.), b our study, C. Bradley et al. 1999 ( P. tenuirostris ), dWarham 1990
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